Perimeter-cooled stage 1 bucket core stabilizing device and related method

ABSTRACT

A core for use in casting a gas turbine bucket, the core comprising a solid upper body portion and a pair of legs extending downwardly from the solid upper body portion, the pair of legs separated by an elongated slot, and a pair of pegs projecting axially from opposite sides of the upper body portion, above the elongated slot but spaced from an upper edge of the upper body portion.

BACKGROUND OF INVENTION

This invention relates generally to the casting of perimeter-cooledbuckets for a gas turbine and, more specifically, to a stabilizationdevice for an internal core used in the bucket casting process.

In an effort to improve the cooling scheme of a stage 1 gas turbinebucket, a “pants-leg” shaped core has been used in the bucket shankportion of the shell die to form a pair of cooling passages in place ofa previous design utilized to form a plurality of radial cooling holes.In the casting process, however, the core tended to drift significantly,resulting in wall thicknesses in the shank portion of the bucket beingout of tolerance.

Core stabilizing devices or “printouts” for improving the yield of abucket casting process have been previously used in stage 2 buckets, butwith a different core design and in a different location relative to theso-called angel wings on the exterior of the shank portion of thebucket. Because of the different design of the stage 1 and stage 2buckets, it was not possible to simply scale up the stage 2 bucket corefor use in the stage 1 bucket casting process.

SUMMARY OF INVENTION

This invention provides stabilization devices on the core used forcasting stage 1 gas turbine buckets. Because of the interiorconfiguration of the shank portion of the bucket, and in light of thedesire to have the stabilizing devices laterally aligned, it wasnecessary to move the stabilizing devices or printouts radiallydownwardly in the shell die so as to be located below the external angelwings of the cast bucket.

It is also a feature of the present invention that the cross sectionalshape of the stabilization devices or printouts is of elliptical ratherthan the oblong or rounded rectangular shape used with the printouts forthe casting of stage 2 buckets. By making the printouts elliptical incross-sectional shape, the flat surfaces of the prior design have beeneliminated, and stresses, particularly at the intersection of theprintouts and the core, have been reduced.

Accordingly, in one aspect, the present invention relates to a core foruse in casting a gas turbine bucket, the core comprising a solid upperbody portion and a pair of legs extending downwardly from the solidupper body portion, the pair of legs separated by an elongated slot, anda pair of pegs projecting axially from opposite sides of the upper bodyportion, above the elongated slot but spaced from an upper edge of theupper body portion.

In another aspect, the invention relates to a core for use in casting agas turbine bucket, the core comprising a solid upper body portion and apair of legs extending downwardly from the solid upper body portion, thepair of legs separated by an elongated slot, and a pair of pegsprojecting axially from opposite sides of the upper body portion, abovethe elongated slot but spaced from an upper edge of the upper bodyportion, and wherein the pegs are elliptical in cross section.

In still another aspect, the invention relates to a method ofcontrolling wall thickness in the shank portion of a turbine bucketduring casting comprising: a) providing a core comprising a solid upperbody portion and a pair of legs extending downwardly from the solidupper body portion, the legs separated by an elongated slot; b)supporting the core within a shell die by a pair of laterally alignedpegs extending from opposite ends of the solid upper body portion, thepegs located above the slot and below an upper edge of the upper bodyportion.

The invention will now be described in connection with the drawingsidentified below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partial cross section of a shank portion of a stage 1 bucketcast n accordance with the invention;

FIG. 2 is a perspective view of a core used in casting the bucket shownin FIG. 1;

FIG. 3 is a front elevation of the core shown in FIG. 2;

FIG. 4 is a rear elevation of the core shown in FIG. 1;

FIG. 5 is a side elevation of the core shown in FIGS. 2-4.

DETAILED DESCRIPTION

With reference to FIG. 1, a stage 1 turbine bucket 10 includes anairfoil portion 12 and a shank portion or shank 14. The shank includes aplurality of so-called angel wings 16, 18 and 20 that serve as sealsvis-a-vis adjacent buckets when installed on the rotor wheel of a gasturbine. The interior of the shank portion includes a hollow space 22,with a central divider 24 that establishes side-by-side cooling passages26 and 28. Elliptical holes 30 and 32 are cast in the fore and aft shankwalls 34 and 36, respectively, as a byproduct of having the coresupported in the shell die during casting.

Turning to FIGS. 2-5, the core 38 has a generally “pants-leg” shape witha solid upper body portion 40 and a pair of radially inwardly extendinglegs 42 and 44 in accordance with an exemplary embodiment of theinvention. A pair of stabilizing pegs or printouts 46, 48 extend axiallyfrom opposite sides of the core while an elongated radially extendingslot 54 separates the pants-leg portions 42 and 44. Notice that the coreis curved in its solid upper portion so as to provide convex and concavesurfaces (50, 52), respectively.

It will be appreciated that in the casting process, the reinforcing pegsor printouts 46, 48 will be supported within aligned holes in the shelldie, thus forming holes 30, 32 in the fore and aft walls of the shankportion of the cast bucket. At the same time, the slot 50 will createthe center partition 24.

By locating the stabilizing pegs or printouts 46, 48 radially below theangel wings 16, 18, sufficient room is provided so that the printouts46, 48 may be directly across from one another, i.e., aligned bothaxially and radially. After the casting process is completed, and thecore removed, holes 30, 32 remain in the bucket and must be plugged. Bylaterally aligning the holes 30, 32, plugs can be inserted and press fitsimultaneously in the holes 30, 32 from opposite directions, withoutcreating any asymmetrical stresses on the bucket.

It is also a feature of this invention, as best seen in FIG. 5, that thestabilizing pegs or printouts 46, 48 have a cross sectional shape thatis elliptical. The elliptical cross-sectional shape reduces stress atthe intersection of the printouts and respective ends of the core byeliminating flat surfaces. When the casting process has been completed,the elliptical holes may be redrilled to a round shape and plugged withcylindrical plugs.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A core for use in casting a gas turbine bucket, the core comprising asolid upper body portion and a pair of legs extending downwardly fromsaid solid upper body portion, said pair of legs separated by anelongated slot, and a pair of pegs projecting axially from oppositesides of the upper body portion, above said elongated slot but spacedfrom an upper edge of said upper body portion.
 2. The core of claim 1wherein said solid upper body portion is curved, forming oppositeconcave and convex surfaces, and said legs are substantially planar,said pegs extending from the convex surface of said solid upper bodyportion.
 3. The core of claim 1 wherein said pegs are elliptical incross section.
 4. The core of claim 2 wherein said pegs are ellipticalin cross section.
 5. The core of claim 1 wherein said solid upper bodyportion has an upper edge, and further wherein, in a radial direction,said pegs are closer to said elongated slot than to said upper edge. 6.The core of claim 1 wherein said pegs are laterally aligned.
 7. A corefor use in casting a gas turbine bucket, the core comprising a solidupper body portion and a pair of legs extending downwardly from saidsolid upper body portion, said pair of legs separated by an elongatedslot, and a pair of pegs projecting axially from opposite sides of theupper body portion, above said elongated slot but spaced from an upperedge of said upper body portion; and wherein said pegs are elliptical incross section.
 8. The core of claim 7 wherein said solid upper bodyportion is curved, forming opposite concave and convex surfaces, andsaid legs are substantially planar, said pegs extending from the convexsurface of said solid upper body portion.
 9. The core of claim 6 whereinsaid pegs are substantially laterally aligned.
 10. A method ofcontrolling wall thickness in the shank portion of a turbine bucketduring casting comprising: a) providing a core comprising a solid upperbody portion and a pair of legs extending downwardly from said solidupper body portion, said legs separated by an elongated slot; b)supporting the core within a shell die by a pair of laterally alignedpegs extending from opposite ends of the solid upper body portion, saidpegs located above said slot and below an upper edge of said upper bodyportion.
 11. The method of claim 10 wherein said solid upper bodyportion is curved, forming opposite concave and convex surfaces, andsaid legs are substantially planar, said pegs extending from the convexsurface of said solid upper body portion.
 12. The method of claim 10wherein said pegs are elliptical in cross section.
 13. The method ofclaim 11 wherein said pegs are elliptical in cross section.
 14. Themethod of claim 10 wherein said solid upper body portion has an upperedge, and further wherein, in a radial direction, said pegs are closerto said elongated slot than to said upper edge.
 15. The method of claim10 wherein said pegs are laterally aligned.